ABSTRACT
Objective: Minor constriction which is the narrowest diameter is considered to be the appropriate apical limit of endodontic treatment. Apex locators provide greater precision, fewer procedural errors, less discomfort to the patient during measurement of working length. The aim of this article is to compare the accuracy of four electronic apex locators in detecting the apical constriction using histological sections as the gold standard. 80Materials and Methods: extracted single-rooted permanent teeth were selected and coronally flattened for stable reference point. Access cavity was prepared and canal patency was checked. Samples were embedded in alginate upto cemento-enamel junction. Working length was determined with the apex locators. A 15 K file adjusted to that reading was placed in the root canal and stabilized with flowable composite. Apical 4 mm of root was longitudinally sectioned and the position of the file in relation to the minor constriction was recorded for each tooth under stereomicroscope at 40X magnification. Chi-square test was carried out to test the difference in accuracy at various levels from the minor foramen. Kruskal Wallis Test was carried out to compare the differences between the study groups for the distance from the tip of the file relative to the minor foramen (P<0.05). Measurements of mean working lengths within ±0.5 mm of minor diameter were 85%Results: acceptable for CanalPro followed by Root ZX Mini (80%) and Propex Pixi (80%) and the least by DPEX V (65%). Conclusion: Accuracy of these instruments for detecting the minor diameter is acceptable for clinical practice